Audiophiles tend to steer clear of stereo Bluetooth headsets, since they don't offer the same fidelity as a good wired set. Last year, the Motorola S9-HD ($99, 3.5 stars) took us by surprise with its clear, bright, and punchy sound, but it wasn't that comfortable to wear. The Motorola S10-HD costs only $79 and offers a step up in comfort. But it's a false economy, as these headphones sound awful.

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Design and Fit
I'll get to the sound quality issues in a moment. First, let's look at the design upgrades. The S10-HD measures 5 by 5.5 by 2 inches (HWD) and weighs 1.5 ounces, a few tenths of an ounce heavier than before. It's made of a mixture of matte plastic and rubber, with clear, soft rubber ear tips. Motorola bills the S10-HD as sweat proof and water resistant, meaning it's fine for exercising or going for a walk in the rain. The speakers themselves are now recessed in their housings, with new ear cushion interfaces and a newly developed hydrophobic acoustic mesh to keep the speakers sweat proof.

The S10-HD's back housing is all new, in an effort to improve outdoor antenna performance. Motorola also revised the button arrangement. A single, small button controls power and pairing duties; it's easier to press than the large, stiff button found on the S9-HD. Each side holds three rubberized buttons down by the ear tip. The right side contains the play, pause, and skip controls, while the left side contains a pair of volume buttons and a multi-function call button. It's still virtually impossible to figure out which button to press without taking off the headset, at least at first.

For this review, I paired the Motorola S10-HD with a Samsung Captivate ($199, 4 stars), a Motorola Flipout ($79.99, 3 stars), and an LG Rumor Touch for Virgin Mobile ($149.99, 4 stars). All three phones paired with the S10-HD on the first try. Overall, the S10-HD was slightly more comfortable to wear than the S9-HD. As before, the S10-HD isn't a true in-ear design, which means it's easier to wear but lets in more extraneous noise from the outside.

That said, there's more flex in the design now, and the ear tips are softer. In addition, the plastic band sits lower on the neck than before. Consequently, it was now possible to sort of lean back in my desk chair without pushing them completely out of position, which was one of the more frustrating aspects of the S9-HD. The S10-HD still moved enough to require readjustment once I laid back in the chair, though. And after about 30 minutes, I still wanted to take the headset off, just like I do with the S9-HD.

Sound Quality, Other Features, and Conclusions
The S10-HD is best when it's powered off; turn it on and everything goes sour. The S10-HD is the worst sounding stereo headset I've tested in some time. Just to make sure, I tried two separate S10-HD units, and they both sounded awful.

I performed back-to-back comparisons with last year's S9-HD, which is one of the best-sounding Bluetooth headsets we've tested. The S9-HD's midbass region is surprisingly full. It also has that same sort of EQed-but-crisp treble you'd expect from industry standards like the venerable Sony MDR-V6 wired headphones, even if the S9-HD is not as detailed or transparent.

The S10-HD, on the other hand, sounds lousy. Even when paired with a brand new Bluetooth 2.1 + EDR device like the Motorola Flipout, the S10-HD sounded closed-in, with a hollow midrange and a flat treble. The same was true on the high-end Samsung Capitvate, as well as on the midrange LG Rumor Touch feature phone. Some older phones still add a layer of fizz and low-volume static to any stereo Bluetooth connection, but even when paired with devices that didn't do that, the S10-HD sounded low-fi.

Bass performance was also worse than before. No matter how I positioned the S10-HD, response seemed to roll off considerably below about 120 Hz. For part of the test, I listened to tracks with prominent kick drums, like Green Day's American Idiot (which has a clicky, roomy kick sound) and Billy Idol's White Wedding (which has a thicker, fuller kick drum with more punch). With both of these tracks, the kick drums almost disappeared entirely in the mix through the S10-HD.

Things fared better once I moved past music. The S10-HD works as a regular Bluetooth headset for making and receiving phone calls. It sounds fine for voice calls. When a call comes in, it pauses the music, and then resumes it once you hang up. You can stream podcasts, audiobooks, and Internet radio. Most mono Bluetooth headsets can't do that, although the latest round of higher-end models we reviewed like the BlueAnt T1 ($59.99, 3.5 stars), the Aliph Jawbone Icon ($99, 4 stars), and the Plantronics Savor M1100 ($99, 3 stars) all have that capability. Motorola claims 9 hours of talk time and 8 hours of music playback on one battery charge.

Audiophiles with extra cash should head for the Nokia BH-905 ($299.95, 3.5 stars); these cans offer genuine noise cancellation, plus a wired mode that offers better fidelity for those times when you're near a headphone jack. Even at a reduced price of $249.99, which I could easily find with a quick Amazon search, the BH-905 aren't for the faint of wallet. But they're more flexible than comparable Bose models thanks to the stereo Bluetooth capability, and (arguably) sound better in wired mode. Beyond that, the Motorola S9-HD offers decent bass, and the Altec Lansing BackBeat 903/906 ($99, 3.5 stars) is more comfortable, with relatively clear sound. Both are better choices than the Motorola S10-HD.

Jamie Lendino is the managing editor of ExtremeTech.com, and has written for PCMag.com and the print magazine since 2005. Recently, Jamie ran the consumer electronics and mobile teams at PCMag, and before that, he was...

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